No abstract

Nonclassical growth mechanisms such as self-assembly and oriented attachment are effective ways to build complex nanostructures from simpler ones. In the latter case, the nanoparticle components are electronically coupled; however, control over the attachment between nanoparticles is highly challenging and generally requires a delicate balance between dipole-, ligand-, and solvent-based interactions. To this end, we perform incomplete cation exchange with Ag (Cu) on CdSe-seeded CdS nanorods and tetrapods to exclusively convert their tips into small AgS (CuS) domains. Selective removal of the ligands from these inorganic domains results in spontaneous, site-specific bridging of the nanoparticles. Using this method, we demonstrate the fabrication of polymer-like linear and branched nanoparticles with enhanced electrical properties, as well as the stoichiometric formation of nanoparticle homo- and heterodimers and tetramers. We show that linked structures can then be completely cation exchanged with Pb to generate PbSe/PbS-based nanostructured photodetector media with enhanced properties.

We use ultrafast coherent two-dimensional electronic spectroscopy (2DES) to study the ultrafast spectral diffusion dynamics of colloidal CdSe quantum dots (QDs) and CdSe nanoplatelets (NPLs). The Center Line Slope (CLS) and Nodal Line Slope (NLS) techniques were employed to analyse the 2DES spectra. We show that no spectral diffusion dynamics occurs for the CdSe QDs. On the other hand, spectral diffusion was observed in the CdSe 5 mono-layers NPLs heavy-hole transition. The normalized Frequency Fluctuation Correlation Function (FFCF) of the CdSe NPLs heavy-hole transition was measured to have a major fast decay component at 140 fs.

between molecular isomers, a phase transition between inorganic solids, or a change in the crystalline phases of liquid crystals. [8] To date, many thermochromic materials have been reported and commercialized, such as leuco dyes, [9] thermotropic liquid crystals, [10][11][12] titanium and vanadium oxides, [13][14][15] and peptide-based polydiacetylene. [16][17][18] Among these examples, the liquid-based leuco dyes and liquid crystals are unique as they can easily be made to fill various shaped voids, can be deposited onto virtually any substrate, and are straightforward to scale-up in terms of production. However, organic dyes have a tendency to suffer from photodegradation, require longer optical path lengths due to a small absorption coefficient (typically ≈10 4 L mol −1 cm −1 ), and possess limited tunability of the T trans . [19] Liquid crystals require a stringent microencapsulation process to avoid degradation and contamination, [20] and the molecules need to be chemically modified in order to tune the T trans . Instead of addressing these limitations directly, we sought to circumvent them by a different approach to traditional liquid-based thermochromics.Herein, we report a liquid-based thermochromic system based on colloidal antimony selenide (Sb 2 Se 3 ) ultrathin nanowires (NWs) that undergo a reversible growth/dissolution process in a Sn 2+ -added amine-thiol mixture. For brevity, we will refer to this liquid thermochromic system as the amine-thiol nanowire (ATNW) solution. Antimony selenide has an optical bulk bandgap of 1.1-1.2 eV, [21] and therefore absorbs wavelengths across the entire visible and near-infrared (NIR) range. It possesses a high absorption coefficient (>10 5 cm −1 ), [22] has low toxicity, and is composed of relatively earth-abundant constituents. As a material that has in recent times been developed for solar cell and photodetector applications, [23] Sb 2 Se 3 nanostructures are resilient toward photodegradation under hours of continuous irradiation and resistant to oxidation under ambient conditions. We find that ATNWs undergo a continuous color change from transparent pale yellow to dark brown when heated and reverse rapidly to pale yellow when cooled. Different from conventional inorganic pigments whose thermochromic properties are based on changes in crystal structure and/or molecular stoichiometry, the color changes in the ATNW solution are due to rapid crystal growth and dissolution. The Sb 2 Se 3 1806164 (2 of 7) www.advmat.de www.advancedsciencenews.com

An overview on the development of wet-chemically synthesized semiconductor nanostructures as optical gain materials is presented in this Review, beginning with the first demonstration of amplified spontaneous emission in zero-dimensional quantum dots and evolving to more sophisticated heterostructures such as one-dimensional core-seeded nanorods, branched core-seeded tetrapods and two-dimensional nanoplatelets. The advantages and challenges of utilizing strongly quantum-confined colloidal semiconductor materials as gain media are discussed, and a concerted effort is made to elaborate on how the progression towards more structurally complex architectures has allowed for dramatic improvements in performance and stability over the archetypal quantum dot.